Radio Communication Device and Radio Communication Method

ABSTRACT

A radio communication device capable of lightening the influence of a frequency selective fading in the wide-band transmission of a single carrier thereby to prevent deterioration of error rate characteristics. In this device, an FFT unit ( 13 ) subjects a modulated signal inputted from a modulation unit ( 12 ) to a Fourier transformation. A pilot insertion unit ( 14 ) inserts a pilot symbol into a plurality of individual frequency components ( 1 -N) of the modulated signal. Weight multiplication units ( 15 - 1, 15 - 2 ) multiply the individual frequency components ( 1 -N) and the pilot symbols inserted into the individual frequency components ( 1 -N), by weight coefficients (W 11 -W 1 N, W 21 -W 2 N) set at a weight coefficient setting unit ( 54 ). IFFT units ( 16 - 1, 16 - 2 ) subject the frequency components ( 1 -N) to an inverse Fourier transformation, thereby to convert the frequency components ( 1 -N) into time domains.

TECHNICAL FIELD

The present invention relates to a radio communication apparatus andradio communication method.

BACKGROUND ART

Looking toward next-generation mobile communication systems, variousstudies have been conducted on radio transmission systems suitable forhigh-speed packet transmission capable of achieving data rates in excessof 100 Mbps. Broadband is necessary for the frequency band used for suchhigh-speed transmission, and the use of a bandwidth on the order of 100MHz has been studied. However, when this kind of broadband transmissionis performed using a single carrier in mobile communications, error ratecharacteristics deteriorate significantly due to multipath interference.Thus, frequency domain equalization has been studied as a technology foreliminating the effects of multipath interference in reproducing awaveform (see Non-patent Document 1, for example). Frequency domainequalization is an equalization technology that can be implemented witha simple configuration, in which equalization processing is performedfor a signal transmitted by means of a single carrier by multiplyingeach frequency component of a received signal received by the inversecharacteristic of a estimation value of propagation path frequencycharacteristic on the receiving side.

Non-patent Document 1: “Frequency domain equalization for single-carrierbroadband wireless systems”, Falconer, D.; Ariyavisitakul, S. L.;Benyamin-Seeyar, A.; Eidson, B.; Communications Magazine, IEEE, Volume:40, Issue: 4, April 2002 Pages: 58-66

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

In single-carrier broadband transmission, if there is a frequencycomponent whose reception level falls significantly due to the effectsof frequency selective fading, equalization is not fully performed and amultipath interference component remains even if the above-describedkind of frequency domain equalization is carried out, with the resultthat error rate characteristics deteriorate.

It is an object of the present invention to provide a radiocommunication apparatus and radio communication method that enable theeffects of frequency selective fading to be reduced and deterioration oferror rate characteristics to be prevented in single-carrier broadbandtransmission.

Means for Solving the Problems

A radio communication apparatus of the present invention employs aconfiguration that includes: a first antenna and a second antenna; afirst conversion section that converts an input signal to the frequencydomain to obtain a plurality of frequency components of the inputsignal; a weighting section that weights the plurality of frequencycomponents using a first weighting factor and weights the plurality offrequency components using a second weighting factor; a secondconversion section that converts the plurality of frequency componentsweighted using the first weighting factor to the time domain to obtain afirst transmit signal and converts the plurality of frequency componentsweighted using the second weighting factor to the time domain to obtaina second transmit signal; and a transmitting section that transmits thefirst transmit signal and the second transmit signal from one or both ofthe first antenna and the second antenna.

ADVANTAGEOUS EFFECT OF THE INVENTION

The present invention enables the effects of frequency selective fadingto be reduced and deterioration of error rate characteristics to beprevented in single-carrier broadband transmission.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the configuration of a radiocommunication apparatus according to Embodiment 1 of the presentinvention;

FIG. 2 is a block diagram showing the configuration of a frequencycharacteristic measuring section according to Embodiment 1 of thepresent invention;

FIG. 3 is a frequency characteristic graph according to Embodiment 1 ofthe present invention;

FIG. 4 is a frequency characteristic graph according to Embodiment 1 ofthe present invention;

FIG. 5 is a frame configuration diagram (TDD system) according toEmbodiment 1 of the present invention;

FIG. 6 is a frame configuration diagram (FDD system) according toEmbodiment 1 of the present invention;

FIG. 7 is a frequency characteristic graph according to Embodiment 2 ofthe present invention;

FIG. 8 is a block diagram showing the configuration of a radiocommunication apparatus according to Embodiment 3 of the presentinvention;

FIG. 9 is a block diagram showing the configuration of a radiocommunication apparatus according to Embodiment 4 of the presentinvention;

FIG. 10 is a block diagram showing the configuration of a radiocommunication apparatus according to Embodiment 5 of the presentinvention;

FIG. 11 is a block diagram showing the configuration of an antennaselection section according to Embodiment 5 of the present invention;and

FIG. 12 is a power amplification characteristic graph according toEmbodiment 5 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will now be described in detailwith reference to the accompanying drawings. A radio communicationapparatus described below is installed, for example, in a radiocommunication terminal apparatus or radio communication base stationapparatus used in a mobile communication system.

Embodiment 1

In the radio communication apparatus shown in FIG. 1, a coding section11 codes input time-series transmit data. A modulation section 12modulates output from coding section 11 using a modulation method suchas QPSK or 16QAM to generate a modulated signal.

An FFT section 13 executes FFT (Fourier transform) processing on amodulated signal input from modulation section 12 to convert themodulated signal to the frequency domain. By means of this FFTprocessing, a plurality of frequency components 1 through N of themodulated signal are obtained. These frequency components 1 through Nare input to a pilot insertion section 14.

Pilot insertion section 14 inserts a frequency-domain pilot symbol ineach of input frequency components 1 through N, and inputs the frequencycomponents to weight multiplication sections 15-1 and 15-2. Details ofthe processing performed by pilot insertion section 14 will be givenlater herein.

Weight multiplication sections 15-1 and 15-2 multiply weighting factorsW11 through W1N and W21 through W2N set by a weighting factor settingsection 54 by frequency components 1 through N and the pilot symbolsinserted in frequency components 1 through N, thereby weightingfrequency components 1 through N and pilot symbols with the sameweighting factor. Weighting factors W11 through W1N multiplied in weightmultiplication section 15-1 and weighting factors W21 through W2Nmultiplied in weight multiplication section 15-2 differ from each other.Frequency components 1 through N weighted by weight multiplicationsection 15-1 are input to an IFFT section 16-1, and frequency components1 through N weighted by weight multiplication section 15-2 are input toan IFFT section 16-2.

IFFT section 16-1 executes IFFT (inverse Fourier transform) processingon input frequency components 1 through N to convert frequencycomponents 1 through N to the time domain. By means of this processing,a transmit signal 1 containing frequency components 1 through N weightedby weights W11 through W1N is obtained. This transmit signal 1 has aguard interval inserted by a GI insertion section 17-1, undergoes radioprocessing such as up-conversion and amplification by a transmit radioprocessing section 18-1, and is then transmitted to a communicatingparty via an antenna 1.

IFFT section 16-2 executes IFFT processing on input frequency components1 through N to convert frequency components 1 through N to the timedomain. By means of this processing, a transmit signal 2 containingfrequency components 1 through N weighted by weights W21 through W2N isobtained. This transmit signal 2 has a guard interval inserted by a GIinsertion section 17-2, undergoes radio processing such as up-conversionand amplification by a transmit radio processing section 18-2, and isthen transmitted to the communicating party via an antenna 2.

On the other hand, a receive radio processing section 51-1 executesradio processing such as down-conversion on a signal received viaantenna 1, and inputs the signal to a pilot extraction section 52-1 anda combining section 55. A receive radio processing section 51-2 executesradio processing such as down-conversion on a signal received viaantenna 2, and inputs the signal to a pilot extraction section 52-2 andcombining section 55.

Pilot extraction section 52-1 extracts a pilot symbol contained in thesignal received by antenna 1 and inputs the pilot symbol to a frequencycharacteristic measuring section 53-1. Frequency characteristicmeasuring section 53-1 measures a frequency characteristic of apropagation path between antenna 1 and the communicating party usingthis pilot symbol. Also, pilot extraction section 52-2 extracts a pilotsymbol contained in the signal received by antenna 2 and inputs thepilot symbol to a frequency characteristic measuring section 53-2.Frequency characteristic measuring section 53-2 measures a frequencycharacteristic of a propagation path between antenna 2 and thecommunicating party using this pilot symbol. The frequencycharacteristic measurement method will be described later herein. Thefrequency characteristics measured by frequency characteristic measuringsections 53-1 and 53-2 are input to weighting factor setting section 54.Weighting factor setting section 54 sets weights W11 through W1N andweights W21 through W2N in accordance with the respective frequencycharacteristics. The setting method will be described later herein.

Combining section 55 combines the signal received by antenna 1 and thesignal received by antenna 2, a demodulation section 56 demodulates thecombined signal, and a decoding section 57 decodes the demodulatedsignal. By this means, receive data is obtained.

Next, the processing performed by frequency characteristic measuringsections 53-1 and 53-2 will be described. Frequency characteristicmeasuring sections 53-1 and 53-2 are composed of an FFT section 531, adivision section 532, and a squaring section 533, as shown in FIG. 2. Bymeans of this configuration, frequency characteristic measuring sections53-1 and 53-2 measure the frequency characteristics of the respectivepropagation paths—that is to say, the propagation path quality of eachfrequency component of the propagation path between antenna 1 and thecommunicating party and the propagation path between antenna 2 and thecommunicating party. Here, the received power value per frequencycomponent of a pilot symbol is measured as the propagation path qualityper frequency component as described below.

FFT section 531 executes FFT processing on an input received pilotsymbol to convert the pilot symbol to the frequency domain. By means ofthis FFT processing, a plurality of frequency components 1 through N ofthe pilot symbol are obtained. These frequency components 1 through Nare input to division section 532. Frequency components 1 through Nobtained here correspond to frequency components 1 through N obtained byFFT section 13. Division section 532 divides each of frequencycomponents 1 through N by frequency characteristic of a pilot replica. Apilot replica is a pilot waveform known to both the pilot symboltransmitting side (that is, the communicating party) and the pilotsymbol receiving side (that is, the radio communication apparatus ofthis embodiment). By means of this division processing, channelestimation values are obtained for each of frequency components 1through N. In squaring section 533, these channel estimation values aresquared to give power values. By having this series of processesperformed by frequency characteristic measuring sections 53-1 and 53-2,received power values are measured for each of frequency components 1through N of the antenna 1 propagation path and the antenna 2propagation path. The measured received power values are input toweighting factor setting section 54.

Next, the processing performed by weighting factor setting section 54will be described. Weighting factor setting section 54 sets weightingfactors W11 through W1N used by weight multiplication section 15-1 andweighting factors W21 through W2N used by weight multiplication section15-2, in accordance with received power values input from frequencycharacteristic measuring section 53-1 (that is, the propagation pathquality of each frequency component of the antenna 1 propagation path)and received power values input from frequency characteristic measuringsection 53-2 (that is, the propagation path quality of each frequencycomponent of the antenna 2 propagation path). As the setting method, areceived power value input from frequency characteristic measuringsection 53-1 and a received power value input from frequencycharacteristic measuring section 53-2 are compared for each of frequencycomponents 1 through N, a weighting factor corresponding to the antennawhere the received power value is larger is set to 1, and a weightingfactor corresponding to the antenna where the received power value issmaller is set to 0. More specifically, for example, among frequencycomponents 1 through N, received power values in frequency component 1transmitted from antenna 1 (that is, the frequency component multipliedby weighting factor W11) and frequency component 1 transmitted fromantenna 2 (that is, the frequency component multiplied by weightingfactor W21) are compared, and if the received power value of frequencycomponent 1 transmitted from antenna 1 is larger than the received powervalue of frequency component 1 transmitted from antenna 2, weightingfactor W11 is set to 1, and weighting factor W21 is set to 0.Conversely, if the received power value of frequency component 1transmitted from antenna 2 is larger than the received power value offrequency component 1 transmitted from antenna 1, weighting factor W21is set to 1, and weighting factor W11 is set to 0. This processing isperformed for all frequency components. By this means, each of frequencycomponents 1 through N is transmitted from one of antenna 1 and antenna2, which has larger received power. That is to say, transmitting antennaselection is performed for each frequency component. By selecting theantenna with the better propagation path quality as the transmittingantenna for each frequency component in this way, a greater transmissiondiversity effect can be achieved.

The above-described comparison/selection processing is illustratedgraphically in FIG. 3. The two curves shown in FIG. 3 represent thefrequency characteristics of each antenna input to weighting factorsetting section 54. As shown in FIG. 3, for each frequency component,the weighting factor corresponding to the antenna with the largerreceived power is set to 1, and the weighting factor corresponding tothe antenna with the smaller received power is set to 0. As a result,the frequency characteristics in signal reception by the communicatingparty are as shown in FIG. 4. That is to say, since one of antenna 1 andantenna 2 which has a better propagation path quality is selected as thetransmitting antenna for each frequency component, there are no longerany frequency components where the communicating party's received powerfalls significantly. AS a result, error rate characteristics can beimproved compared with a case in which all frequency components aretransmitted only from either antenna 1 or antenna 2.

Next, the processing performed by pilot insertion section 14 will bedescribed. FIG. 5 applies to a TDD system, and FIG. 6 to an FDD system.

As shown in FIG. 5 and FIG. 6, in this embodiment each frame is dividedinto a plurality of time slots, and pilot symbols are transmitted in thestart time slot and end time slot of each frame. Thus, in pilotinsertion section 14, pilot symbols are inserted in each frequencycomponent by having a switch corresponding to each frequency componentconnected to an “a” side at transmission timings of start time slot andend time slot, and to a “b” side at other timings. Also, in a TDDsystem, weighting factor updating in weighting factor setting section 54is performed at the boundary between an uplink frame and downlink frame,as shown in FIG. 5, and the same weighting factor is used in all slotsin one downlink frame. In an FDD system, on the other hand, weightingfactor updating in weighting factor setting section 54 is performed atthe boundary between each frame, as shown in FIG. 6, and the sameweighting factor is used in all slots in one frame. By using suchweighting factor update timing, a pilot part and data part aremultiplied by the same weighting factor, so that in signal reception bya communicating party, the communicating party can receive a signal bymeans of the same kind of reception processing as when all frequencycomponents are transmitted from only one antenna, as in the prior art.

Thus, according to this embodiment, a transmission diversity effect canbe obtained for each frequency component, enabling a fall in power offrequency component due to the effects of frequency selective fading tobe reduced, and as a result, enabling error rate characteristics to beimproved. Also, since a weighting factor is set for each frequencycomponent in accordance with propagation path frequency characteristics,transmission diversity effects can be further increased.

It is also possible for the communicating party to measure thepropagation path quality of frequency components of each antenna andreport the results to the radio communication apparatus of thisembodiment, and for the radio communication apparatus to set a weightingfactor in accordance with a reported propagation path quality. And it isalso possible for the communicating party additionally to performweighting factor setting in accordance with propagation path quality andreport the results to the radio communication apparatus of thisembodiment, and for the radio communication apparatus to multiply eachfrequency component by a reported weighting factor. In this way, theradio communication apparatus of this embodiment can be given an optimalconfiguration for an FDD system that uses propagation path of differentfrequencies for transmission and reception.

Embodiment 2

A radio communication apparatus according to this embodiment sets aweighting factor combination as a weighting factor multiplied by eachfrequency component, among a plurality of combinations of weightingfactors W11 through W1N and W21 through W2N, where received power islargest at the communicating party that is the signal receiving side, inaccordance with the propagation path quality of each frequencycomponent.

A radio communication apparatus according to this embodiment differsfrom Embodiment 1 only in the operation of weighting factor settingsection 54. When signals are transmitted from a plurality of antennas, aweighting factor whereby signals transmitted from each antenna arereinforced at the reception point is a weighting factor having anamplitude and phase such that P_(n) expressed by Equation (1) is amaximum. Thus, weighting factor setting section 54 sets a weightingfactor combination w_(n) where P_(n) of Equation (1) is a maximum as theweighting factors of the frequency components of each antenna. Aplurality of weighting factor combination w_(n) candidates are storedbeforehand in weighting factor setting section 54, and weighting factorsetting section 54 calculates P_(n) for these combination candidates,selects the combination w_(n) where P_(n) is a maximum, and outputs thisselected combination w_(n) to weight multiplication sections 15-1 and15-2.

P_(n)=w_(n) ^(H)H_(n) ^(H)H_(n)w_(n)  (1)

w_(n)=[w_(1n),w_(2n)]^(T),H_(n)=[h_(1n)h_(2n)]

Here, h_(1n) represents the propagation path quality of frequencycomponent n of antenna 1, and h_(2n) represents the propagation pathquality of frequency component n of antenna 2. ^(H) represents a complexconjugate transposition, and ^(T) a transposition. P_(n) is a valueproportional to the received power when a signal transmitted aftermultiplication by weighting factor w_(n) is received by thecommunicating party via a propagation path of propagation path qualityH_(n). Examples of w_(n) candidates are those with either of {0.2, 0.8}as the amplitude and any of {0, π/4, 2π/4, 3π/4, 4π/4, 5π/4, 6π/4, 7π/4}as the phase.

FIG. 7 shows frequency characteristics at the time of signal receptionby the communicating party when weighting factor setting according tothis embodiment is performed. It can be seen from FIG. 7 that whenweighting factor setting according to this embodiment is performed,frequency components whose received power falls significantly areeliminated. Comparing FIG. 7 with FIG. 4 (Embodiment 1), received poweris smaller in FIG. 7 than in FIG. 4. However, if the estimation error offrequency characteristic of propagation path is large, larger receivedpower is obtained by transmission of each frequency component from twoantennas than by transmission from one antenna as in Embodiment 1.

Thus, according to this embodiment, received power can be reinforced foreach frequency component, so that frequency components whose receivedpower falls significantly are eliminated, and, as a result, error ratecharacteristics can be improved.

Embodiment 3

In Embodiment 1, a signal is deformed on an individual frequencycomponent basis for each antenna by means of weighting factormultiplication, and there is consequently a possibility of a signal'sPAPR (Peak to Average Power Ratio) becoming large compared with a casein which multiplication by a weighting factor is not performed. Thispossibility is greatly increased by creating non-transmitted frequencycomponents in the frequency components within a signal. In the case of alarge PAPR that comes within the nonlinear region of the transmittingamplifier characteristic, a transmit signal is distorted and the SNRdeteriorates on the signal receiving side.

Thus, in this embodiment, the degree of signal deformation is reduced bytransmitting only a frequency component where the difference inpropagation path quality between antennas is greater than or equal to athreshold value from one antenna, and transmitting a frequency componentwhere that difference is less than the threshold value from a pluralityof antennas, thereby reducing the number of non-transmitted frequencycomponents in signals transmitted from each antenna.

The configuration of a radio communication apparatus according to thisembodiment is shown in FIG. 8. In the following description,configuration elements identical to those in Embodiment 1 (FIG. 1) areassigned the same reference numbers as in Embodiment 1, and descriptionsthereof are omitted.

In the radio communication apparatus shown in FIG. 8, frequencycharacteristic measuring section 53-1 measures the received power valuesof frequency components 1 through N of a pilot symbol contained in asignal received by antenna 1, and inputs the received power values toweighting factor setting section 54 and a power difference measuringsection 58. Also, frequency characteristic measuring section 53-2measures the received power values of frequency components 1 through Nof a pilot symbol contained in a signal received by antenna 2, andinputs the received power values to weighting factor setting section 54and power difference measuring section 58.

Power difference measuring section 58 measures the difference betweenthe received power value input from frequency characteristic measuringsection 53-1 and the received power value input from frequencycharacteristic measuring section 53-2 for each frequency component. Thatis to say, power difference measuring section 58 measures the differencein the received power value of each frequency component between antenna1 and antenna 2. This received power difference is input to a thresholdvalue determination section 59.

Threshold value determination section 59 determines for each frequencycomponent whether or not the received power difference input from powerdifference measuring section 58 is greater than or equal to a thresholdvalue, and inputs the determination result to weighting factor settingsection 54.

Weighting factor setting section 54 sets a weighting factor for thefrequency component where the received power difference is determined tobe greater than or equal to the threshold value using the setting methoddescribed in Embodiment 1. That is to say, weighting factor settingsection 54, between antenna 1 and antenna 2, compares the received powervalues of a frequency component where the received power difference isdetermined to be greater than or equal to the threshold value, sets theweighting factor of the antenna where the received power value is largerto 1, and sets the weighting factor of the antenna where the receivedpower value is smaller to 0. On the other hand, for a frequencycomponent where the received power difference is determined to be lessthan the threshold value, weighting factor setting section 54 sets theweighting factor to 0.5 for both antennas. By performing this kind ofweighting factor setting, only a frequency component where the receivedpower difference is large—that is, only a frequency component where thedifference in propagation path quality between the antennas is large—istransmitted from the antenna with the better propagation path quality,and other frequency components are transmitted from both antennas. Thus,the number of frequency components transmitted from only one antenna canbe decreased, and the degree of signal deformation is reduced. By thismeans, an increase in the PAPR can be suppressed.

Thus, according to this embodiment, since deformation of frequencycomponents at each antenna is kept to a minimum, an increase in the PAPRcan be suppressed, and deterioration of error rate characteristicscaused by signal deformation due to an increase in the PAPR can besuppressed. Also, frequency components having a large difference inpropagation path quality can be transmitted from the antenna with thebetter propagation path quality with concentrated power, so that at thesignal receiving side, frequency components whose received power fallssignificantly is eliminated, and it is possible to improve error ratecharacteristics.

Weighting factor setting section 54 of this embodiment may also use thesetting method described in Embodiment 2 to set the weighting factor ofa frequency component where the received power difference is determinedto be greater than or equal to a threshold value.

Embodiment 4

In this embodiment, a radio communication apparatus is described thatsuppresses an increase in the PAPR by means of a different method fromthat in Embodiment 3.

The configuration of a radio communication apparatus according to thisembodiment is shown in FIG. 9. In the following description,configuration elements identical to those in Embodiment 1 (FIG. 1) areassigned the same reference numbers as in Embodiment 1, and descriptionsthereof are omitted.

In the radio communication apparatus shown in FIG. 9, frequencycharacteristic measuring section 53-1 measures the received power valuesof frequency components 1 through N of a pilot symbol contained in asignal received by antenna 1, and inputs the received power values toweighting factor setting section 54 and a peak suppression frequencysetting section 60. Also, frequency characteristic measuring section53-2 measures the received power values of frequency components 1through N of a pilot symbol contained in a signal received by antenna 2,and inputs the received power values to weighting factor setting section54 and peak suppression frequency setting section 60.

Peak suppression frequency setting section 60 compares the receivedpower values of a plurality of frequency components between theantennas, and of the plurality of frequency components, sets a frequencycomponent where the received power value of one antenna is lower by apredetermined value or more than the received power value of the otherantenna as a peak suppression frequency component. If the PAPR of apost-IFFT signal is greater than or equal to a threshold value, a signalfor suppressing peak power (peak suppression signal) is inserted in thispeak suppression frequency component. Then, peak suppression frequencysetting section 60 inputs the setting result to peak suppression signalgeneration sections 21-1 and 21-2, and peak suppression signal insertionsections 22-1 and 22-2. When a peak suppression frequency component isset in this way, a frequency component in which a peak suppressionsignal is inserted becomes a frequency component multiplied by aweighting factor of 0 in Embodiment 1, and also becomes a frequencycomponent that is transmitted from an antenna whose propagation pathquality is considerably lower than that of the other antenna and suffersmajor propagation path attenuation, enabling an increase in the PAPR tobe suppressed without causing deterioration of reception quality on thecommunicating party side due to the effects of the peak suppressionsignal.

On the other hand, PAPR measuring sections 19-1 and 19-2 provided foreach antenna measure the PAPR value of a post-IFFT signal and input thisvalue to threshold value determination sections 20-1 and 20-2, and peaksuppression signal generation sections 21-1 and 21-2. Also, PAPRmeasuring sections 19-1 and 19-2 report the position on the time axis atwhich peak power occurred to peak suppression signal generation sections21-1 and 21-2.

Threshold value determination sections 20-1 and 20-2 compare the inputPAPR value with a threshold value, and if the PAPR value is greater thanor equal to the threshold value, output a directive to generate a peaksuppression signal to peak suppression signal generation sections 21-1and 21-2.

In accordance with this directive, peak suppression signal generationsections 21-1 and 21-2 generate a peak suppression signal. Based on theposition on the frequency axis of a frequency component set for peaksuppression and the position of peak power on the time axis, peaksuppression signal generation sections 21-1 and 21-2 generate a peaksuppression signal with a phase such that that frequency componentsignal has the opposite phase at the peak power position on the timeaxis. Also, peak suppression signal generation sections 21-1 and 21-2make the amplitude of the peak suppression signal a value proportionalto the PAPR value. Another peak suppression signal generation methodthat can be used is the method described in Unexamined Japanese PatentPublication No. 2001-237800, for example. Peak suppression signalgeneration sections 21-1 and 21-2 then input the generated peaksuppression signals to peak suppression signal insertion sections 22-1and 22-2.

Peak suppression signal insertion sections 22-1 and 22-2 insert the peaksuppression signal generated by peak suppression signal generationsections 21-1 and 21-2 respectively in a frequency component set by peaksuppression frequency setting section 60.

Thus, according to this embodiment, an increase in the PAPR can besuppressed without causing deterioration of reception quality on thecommunicating party side due to peak suppression signal insertion, anddeterioration of error rate characteristics due to signal distortioncaused by an increase in the PAPR can be suppressed.

Embodiment 5

In this embodiment, a radio communication apparatus is described thatsuppresses an increase in the PAPR by means of a different method fromthose in Embodiments 3 and 4.

The configuration of a radio communication apparatus according to thisembodiment is shown in FIG. 10. In the following description,configuration elements identical to those in Embodiment 1 (FIG. 1) areassigned the same reference numbers as in Embodiment 1, and descriptionsthereof are omitted.

In the radio communication apparatus shown in FIG. 10, if the PAPR of apost-IFFT signal is greater than or equal to a threshold value, anantenna selection section 23 combines a signal that has undergone IFFTprocessing by IFFT section 16-1 and a signal that has undergone IFFTprocessing by IFFT section 16-2, and selects either antenna 1 or antenna2 as the transmitting antenna for this combined signal. Antennaselection section 23 selects the antenna where the total power of allfrequency components (that is, the total value of the propagation pathqualities of all frequency components) is larger as the transmittingantenna.

The internal configuration of antenna selection section 23 is shown inFIG. 11. In FIG. 11, a PAPR measuring section 231 measures the PAPRvalue of a post-IFFT signal input from IFFT section 16-1 (the PAPR valueof antenna 1) and the PAPR value of a post-IFFT signal input from IFFTsection 16-2 (the PAPR value of antenna 2), and inputs the PAPR valuesto a threshold value determination section 232.

Threshold value determination section 232 compares the antenna 1 PAPRvalue and the antenna 2 PAPR value with a threshold value, and if bothPAPR values are less than the threshold value, connects SW1 through SW4to the “a” side. Thus, when the antenna 1 PAPR value and antenna 2 PAPRvalue are both greater than or equal to the threshold value, in the sameway as in Embodiment 1, a signal output from IFFT section 16-1 is inputdirectly to GI insertion section 17-1, and a signal output from IFFTsection 16-2 is input directly to GI insertion section 17-2.

On the other hand, if either the antenna 1 PAPR value or the antenna 2PAPR value is greater than or equal to the threshold value, thresholdvalue determination section 232 connects SW1 through SW4 to the “b”side, and also instructs a received power measuring section 234 tooperate. Thus, in this case, a signal output from IFFT section 16-1 anda signal output from IFFT section 16-2 are both input to a combiningsection 233, and combining section 233 combines these two signals. Thecombined signal is output to SW5.

A pilot symbol extracted by pilot extraction section 52-1 and a pilotsymbol extracted by pilot extraction section 52-2 are input to receivedpower measuring section 234. In accordance with a directive fromthreshold value determination section 232, received power measuringsection 234 measures the received power values of these pilot symbols(the received power value of antenna 1 and the received power value ofantenna 2) in the time domain, and inputs the received power values to atransmitting antenna selection section 235. Thus, if the antenna 1 PAPRvalue and antenna 2 PAPR value are both less than the threshold value,received power measuring section 234 does not operate, and unnecessarypower consumption is prevented. As the received power value measured inthe time domain by received power measuring section 234 is the totalpower value for all frequency components, it is also possible for thetotal values of the received power of all frequency components measuredby frequency characteristic measuring sections 53-1 and 53-2 to be usedrespectively as the antenna 1 received power value and the antenna 2received power value.

Transmitting antenna selection section 235 compares the antenna 1received power value and antenna 2 received power value, and selects theantenna with the larger received power value. If the antenna 1 receivedpower value and antenna 2 received power value are equal, antenna 1 isselected. That is to say, transmitting antenna selection section 235connects SW5 to the “a” side if the antenna 1 received power value isgreater than or equal to the antenna 2 received power value, andconnects SW5 to the “b” side if the antenna 2 received power value isgreater than the antenna 1 received power value. By this means, wheneither the antenna 1 PAPR value or the antenna 2 PAPR value is greaterthan or equal to the threshold value, the signal combined by combiningsection 233 is transmitted from either antenna 1 or antenna 2.

Next the method of setting the threshold value used by threshold valuedetermination section 232 will be described. When the poweramplification characteristic of the transmitting amplifiers of transmitradio processing sections 18-1 and 18-2 is as shown in FIG. 12,distortion occurs in a transmit signal if the PAPR comes within thenonlinear region of the amplifier characteristic. Therefore, to preventtransmit signal distortion, the PAPR threshold value used by thresholdvalue determination section 232 is set to an input backoff powervalue—that is, a marginal power value from the average level in thelinear region.

A signal following combining by combining section 233 is the same as thesignal input from modulation section 12 to FFT section 13. Thus, in thisembodiment, it is also possible to use a configuration whereby, ifeither the antenna 1 PAPR value or the antenna 2 PAPR value is greaterthan or equal to a threshold value, the signal input to FFT section 13is transmitted directly instead of the combined signal.

Thus, according to this embodiment, the occurrence of nonlineardistortion in a transmit signal due to an increase in the PAPR can beprevented. Also, a signal is transmitted from the antenna with the bestpropagation path quality for each frequency component only whennonlinear distortion does not occur, enabling an improvement inreception quality to be achieved dependably on the signal receivingside.

In the above embodiments, a radio communication terminal apparatus maybe indicated by “UE,” and a radio communication base station apparatusby “Node B.”

In the above embodiments, a signal transmitted from a radiocommunication apparatus may be, in addition to a signal transmitted bymeans of a single carrier, an IFDMA (Interleaved Frequency DivisionMultiple Access) signal having frequency components distributed at equalintervals, a Distributed FDMA signal, or a Localized FDMA signal using alocalized band.

The function blocks used in the descriptions of the above embodimentsare typically implemented as LSIs, which are integrated circuits. Thesemay be implemented individually as single chips, or a single chip mayincorporate some or all of them.

Here, the term LSI has been used, but the terms IC, system LSI, superLSI, and ultra LSI may also be used according to differences in thedegree of integration.

The method of implementing integrated circuitry is not limited to LSI,and implementation by means of dedicated circuitry or a general-purposeprocessor may also be used. An FPGA (Field Programmable Gate Array) forwhich programming is possible after LSI fabrication, or a reconfigurableprocessor allowing reconfiguration of circuit cell connections andsettings within an LSI, may also be used.

In the event of the introduction of an integrated circuit implementationtechnology whereby LSI is replaced by a different technology as anadvance in, or derivation from, semiconductor technology, integration ofthe function blocks may of course be performed using that technology.The adaptation of biotechnology or the like is also a possibility.

The present application is based on Japanese Patent Application No.2004-224657 filed on Jul. 30, 2004, entire content of which is expresslyincorporated herein by reference.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use in a radio communication basestation apparatus or radio communication terminal apparatus used in amobile communication system or the like.

1. A radio communication apparatus comprising: a first antenna and a second antenna; a first conversion section that converts an input signal to a frequency domain to obtain a plurality of frequency components of the input signal; a weighting section that weights the plurality of frequency components using a first weighting factor and weights the plurality of frequency components using a second weighting factor; a second conversion section that converts the plurality of frequency components weighted using the first weighting factor to a time domain to obtain a first transmit signal and converts the plurality of frequency components weighted using the second weighting factor to the time domain to obtain a second transmit signal; and a transmitting section that transmits the first transmit signal and the second transmit signal from one or both of the first antenna and the second antenna.
 2. The radio communication apparatus according to claim 1, further comprising a measuring section that measures a first propagation path quality of the first antenna and a second propagation path quality of the second antenna for each of the plurality of frequency components, wherein the weighting section sets the first weighting factor and the second weighting factor in accordance with the first propagation path quality and the second propagation path quality.
 3. The radio communication apparatus according to claim 2, wherein the weighting section compares the first propagation path quality and the second propagation path quality for each of the plurality of frequency components, and sets one of the first weighting factor and the second weighting factor to 1 and sets the other to 0 for each of the plurality of frequency components in accordance with a comparison result.
 4. The radio communication apparatus according to claim 3, wherein the weighting section sets one of the first weighting factor and the second weighting factor to 1 and sets the other to 0 only for a frequency component where a difference between the first propagation path quality and the second propagation path quality is greater than or equal to a threshold value.
 5. The radio communication apparatus according to claim 2, wherein the weighting section has a plurality of combinations of the first weighting factor and the second weighting factor, and in accordance with the first propagation path quality and the second propagation path quality, selects a combination among the plurality of combinations such that received power on a signal receiving side becomes maximum to set the first weighting factor and the second weighting factor.
 6. The radio communication apparatus according to claim 2, wherein the measuring section measures received power of each of a plurality of frequency components of a signal received by the first antenna as the first propagation path quality and measures received power of each of a plurality of frequency components of a signal received by the second antenna as the second propagation path quality.
 7. The radio communication apparatus according to claim 1, further comprising an insertion section that inserts a pilot symbol in each of the plurality of frequency components, wherein the weighting section weights the pilot symbol using the same weighting factor as used for the plurality of frequency components.
 8. The radio communication apparatus according to claim 1, further comprising: a measuring section that measures a first propagation path quality of the first antenna and a second propagation path quality of the second antenna for each of the plurality of frequency components; and an insertion section that inserts a signal for suppressing peak power in a frequency component where one of the first propagation path quality and the second propagation path quality is lower than the other by a predetermined value or more among the plurality of frequency components.
 9. The radio communication apparatus according to claim 1, wherein the transmitting section, when a peak to average power ratio is greater than or equal to a threshold value, transmits a combined signal combining the first transmit signal and the second transmit signal or the input signal from one of the first antenna and the second antenna.
 10. The radio communication apparatus according to claim 9, wherein the transmitting section transmits the combined signal from an antenna, of the first antenna and the second antenna, where a total of propagation path qualities of the plurality of frequency components is larger.
 11. A radio communication base station apparatus comprising the radio communication apparatus according to claim
 1. 12. A radio communication terminal apparatus comprising the radio communication apparatus according to claim
 1. 13. A radio communication method comprising: a first conversion step of converting an input signal to a frequency domain to obtain a plurality of frequency components of the input signal; a weighting step of weighting the plurality of frequency components using a first weighting factor and weighting the plurality of frequency components using a second weighting factor; a second conversion step of converting the plurality of frequency components weighted using the first weighting factor to a time domain to obtain a first transmit signal and converting the plurality of frequency components weighted using the second weighting factor to a time domain to obtain a second transmit signal; and a transmitting step of transmitting the first transmit signal and the second transmit signal from one or both of the first antenna and the second antenna. 